Composite board based on hydrated calcium silicate and polycrystalline fibers and method of preparation

Abstract

The application discloses a kind of based on hydration calcium silicate and polycrystalline fiber composite board and preparation method, belong to inorganic fireproof heat insulation board technical field. Including board body, the board body is by following component weight parts constitutes: calcium source 25-45 parts, silicon source 30-55 parts, polycrystalline fiber 5-25 parts, interface modifier 0.5-3 parts, dispersing agent 0.1-1 part, foam stabilizer 0.1-0.5 parts, water 150-300 parts;The calcium source and silicon source hydrothermal reaction generate hydration calcium silicate crystal, the hydration calcium silicate crystal is mutually interwoven and forms porous matrix skeleton, the polycrystalline fiber disperses in the porous matrix skeleton, the hydration calcium silicate crystal in-situ growth on polycrystalline fiber surface, and forms chemical combination layer with polycrystalline fiber.The based on hydration calcium silicate and polycrystalline fiber composite board and preparation method of the application, the prepared board has excellent fireproof heat insulation performance, while having good mechanical toughness, impact resistance and high temperature long-term stability.

Description

Technical Field

[0001] This invention specifically relates to a composite board based on hydrated calcium silicate and polycrystalline fiber and its preparation method, belonging to the technical field of inorganic fireproof and heat-insulating boards. Background Technology

[0002] Microporous calcium silicate boards are widely used as fireproof and heat-insulating materials in industrial and construction fields due to their extremely low thermal conductivity and A1-level non-combustibility. Traditional microporous calcium silicate boards mainly form a porous structure by interweaving calcium silicate hydrate crystals (such as tobermorite and hard calcium silicate) through hydrothermal synthesis. However, their brittleness, low flexural strength, and poor impact resistance limit their application in situations requiring a certain degree of flexibility and seismic resistance. In addition, aluminosilicate fiber felt or boards have excellent flexibility and high-temperature stability, but when used alone as boards, they have low structural strength, are prone to powdering, and pure fiber products are at risk of powdering and shrinkage deformation under long-term high-temperature cycling conditions, which cannot meet the requirements of structural load-bearing and long-term service. Therefore, some processes incorporate fibers into the calcium silicate matrix to improve toughness, such as the high-strength, lightweight, integral hydrophobic hard calcium silicate disclosed in Chinese Patent Publication No.: CN102825650A. The manufacturing method of stone-insulated fireproof boards: This type of fireproof insulation board has high strength, uniform material, no air bubbles, and light weight; however, it generally has the following defects: First, the fibers are prone to agglomeration in high-solids slurry, resulting in poor dispersion uniformity and large fluctuations in material performance; Second, the fibers and calcium silicate matrix are only physically wrapped, and the interface between the fibers and the matrix is ​​still abruptly bonded, which can easily lead to fiber pull-out and matrix cracking under stress, with limited improvement in toughness; Third, the incorporation of fibers often leads to an increase in material density and destruction of the pore structure, making it impossible to balance low density, low thermal conductivity, and high strength. Moreover, ordinary glassy fibers are prone to softening and pulverizing at high temperatures, which cannot improve the high-temperature service stability of the material; Finally, a single nanoporous structure cannot achieve a deep balance between density and thermal insulation performance. If the density is further reduced, the porosity needs to be increased, which can easily lead to the collapse of the matrix skeleton and a significant decrease in mechanical strength, failing to meet the load-bearing requirements. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes a composite board based on hydrated calcium silicate and polycrystalline fibers, along with its preparation method. The composite board possesses excellent fire-resistant and heat-insulating properties, as well as good mechanical toughness, impact resistance, and long-term high-temperature stability.

[0004] The present invention relates to a composite board based on hydrated calcium silicate and polycrystalline fibers, comprising a board body composed of the following components by weight: 25-45 parts calcium source, 30-55 parts silicon source, 5-25 parts polycrystalline fibers, 0.5-3 parts interface modifier, 0.1-1 parts dispersant, 0.1-0.5 parts foam stabilizer, and 150-300 parts water. The calcium source and silicon source undergo a hydrothermal reaction to generate hydrated calcium silicate crystals, which interweave to form a porous matrix framework. The polycrystalline fibers are dispersed in the porous matrix framework, and the hydrated calcium silicate crystals and polycrystalline fibers form a three-dimensional interpenetrating network structure inside the board. The hydrated calcium silicate crystals grow in situ on the surface of the polycrystalline fibers, forming a chemical bonding layer with the polycrystalline fibers.

[0005] Further, the calcium source is one or more of calcium oxide, calcium hydroxide, and carbide slag, and the effective calcium oxide content in the calcium source is ≥85% by mass; the silicon source is one or more of silica fume, silica, fly ash, diatomaceous earth, and quartz powder, and the active silica content in the silicon source is ≥80% by mass, with a particle size D50 of 1~10μm; the polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber; the polycrystalline fiber has a diameter of 25μm, a length of 15mm, and a crystalline phase composition of... The content of polycrystalline fiber is ≥95%; the polycrystalline fiber is a modified polycrystalline fiber that has undergone surface modification treatment, wherein the surface modification treatment is silane coupling agent modification treatment or calcium hydroxide saturated solution hydration modification treatment; the interface modifier is one or more of silane coupling agent, aluminate coupling agent and titanate coupling agent; the dispersant is one or more of polycarboxylate dispersant, naphthalene sulfonate dispersant, sodium tripolyphosphate and sodium hexametaphosphate; the foam stabilizer is one or more of calcium stearate, sodium stearate, sodium dodecyl sulfate and methylcellulose.

[0006] Furthermore, the porous matrix framework has a porosity of 60%-85% and an average pore size of 50-200 nm.

[0007] Furthermore, the sheet material further includes 0.05-0.3 parts of a controllable foaming agent; the polycrystalline fiber is a polycrystalline hybrid reinforcing phase formed by mixing long polycrystalline fibers, short polycrystalline fibers, and mullite whiskers, wherein the short polycrystalline fibers and long polycrystalline fibers are composed of fibers of the same material, the crystalline phase mass content of the mullite whiskers is ≥95%, and the mass ratio of the long polycrystalline fibers, short polycrystalline fibers, and mullite whiskers is 5~8:2~3:1~2; the hydrated calcium silicate crystals interweave to form a hierarchical closed-cell porous matrix framework, and the polycrystalline hybrid reinforcing phase is dispersed in the hierarchical closed-cell porous matrix framework; a hydrated calcium silicate nanocrystal seed transition layer is provided on the surface of the polycrystalline hybrid reinforcing phase, and the hydrated calcium silicate crystals grow directionally in situ on the fiber surface through the hydrated calcium silicate nanocrystal seed transition layer, forming a continuous gradient chemical bonding layer with the polycrystalline hybrid reinforcing phase.

[0008] The gradient chemical bonding layer undergoes a two-step pretreatment process. First, the hybrid reinforcing phase is hydroxylated and etched to introduce a large number of active hydroxyl groups onto the surface. Then, a uniform layer of hydrated calcium silicate nanocrystal seed is deposited in situ on the fiber surface using a calcium-silicon precursor solution, forming a continuous gradient transition interface. During the hydrothermal reaction, the hydrated calcium silicate crystals of the matrix grow directionally using the nanocrystal seed sites and integrate with the transition layer, achieving continuous chemical bonding from the polycrystalline fiber to the matrix hydrated calcium silicate, eliminating interfacial stress concentration, and significantly improving the interfacial bonding strength.

[0009] The hierarchical closed-cell structure of the hierarchical closed-cell porous matrix framework is controlled as follows: First-level nanopores are formed by regulating the foam stabilizer, which restricts the convection and thermal conduction of air molecules and achieves basic low thermal conductivity; Second-level micron closed pores are formed by the decomposition and release of gas by the controllable foaming agent during hydrothermal heating, which reduces the proportion of solid-phase framework, reduces material density and solid-phase thermal conductivity, and at the same time, the closed-cell structure can avoid air convection, further reducing the thermal conductivity; The two levels of pores work together to significantly reduce density while maintaining mechanical strength through the optimization of the framework structure, achieving a balance between density and thermal insulation performance.

[0010] Polycrystalline hybrid reinforcing phase achieves ternary hybrid reinforcement and toughening: long polycrystalline fibers construct a macroscopic three-dimensional skeleton, bear the main load, and improve the overall flexural strength of the material; short polycrystalline fibers fill the gaps between long fibers, refine the matrix grains, and reduce defects inside the matrix; mullite whiskers form bridges between fibers and the matrix, and pin and deflect microcracks inside the matrix, consuming the energy of crack propagation; through full-scale crack control at the macro, meso, and micro scales, the fracture toughness and impact resistance of the material are significantly improved.

[0011] Furthermore, the controllable foaming agent is one or more of ammonium bicarbonate and sodium bicarbonate; the nanocrystalline seed transition layer is a porous active layer formed by uniform deposition of hydrated calcium silicate nanocrystals; and the thickness of the nanocrystalline seed transition layer is 50-200 nm.

[0012] Furthermore, the hierarchical closed-pore porous matrix framework includes primary nanopores and secondary micron-sized closed pores; the primary nanopores have a pore size of 50-200 nm and a porosity of 70%-80%; the secondary micron-sized closed pores have a pore size of 1-5 μm and a porosity of 20%-30%.

[0013] Furthermore, the long polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber, with a diameter of 2-5 μm, a length of 3-5 mm, and a crystalline phase mass content ≥95%; the short polycrystalline fiber is the same material as the long polycrystalline fiber, with a diameter of 2-5 μm, a length of 0.5-1 mm, and a crystalline phase mass content ≥95%; the mullite whisker has a diameter of 0.1-0.5 μm, a length of 5-20 μm, and an aspect ratio ≥20.

[0014] A method for preparing a composite board based on hydrated calcium silicate and polycrystalline fibers, the method comprising the following steps: S1. Polycrystalline fiber pretreatment: Surface modification treatment is performed on polycrystalline fibers to obtain modified polycrystalline fibers; S2. Preparation of composite slurry: Calcium source is added to water for digestion treatment, and after sieving, calcium hydroxide emulsion is obtained; silicon source and dispersant are added to the calcium hydroxide emulsion, and stirred evenly to obtain matrix mixture slurry; modified polycrystalline fiber is added to the matrix mixture slurry, dispersed evenly, interface modifier and foam stabilizer are added, and stirred evenly to obtain composite slurry; S3. Molding: The composite slurry is shaped to obtain a wet blank; S4. Hydrothermal synthesis: The wet green body is placed in a reaction vessel and a hydrothermal synthesis reaction is carried out to allow hydrated calcium silicate crystals to grow in situ on the surface of polycrystalline fibers, thereby obtaining the green body after the reaction. S5. Drying and shaping: The reacted green body is dried in steps to obtain the finished sheet body.

[0015] Further, the surface modification treatment is a silane coupling agent modification treatment, specifically: immersing the polycrystalline fiber in a 1%-5% (w / w) silane coupling agent ethanol solution for 30-60 minutes, then drying at 80-120℃ for 24 hours to obtain modified polycrystalline fiber; or the surface modification treatment is a calcium hydroxide saturated solution hydration modification treatment, specifically: immersing the polycrystalline fiber in a calcium hydroxide saturated solution for 2-4 hours, then removing and draining to obtain modified polycrystalline fiber; the digestion treatment temperature is 40-60℃, the time is 15-30 minutes, and sieving is done using a 200-mesh sieve; the dispersion rotation speed is 1000-3000 rpm. The temperature is 00 rpm, and the time is 10-30 min; the water-solid ratio of the composite slurry is 3:1~6:1; the molding is one of compression molding, sheet forming, or casting; wherein the compression molding pressure is 0.5-2 MPa, and the holding time is 10-30 s; during the hydrothermal synthesis, the reactor filling degree is 30%-50%, the heating rate is 12℃ / min, the reaction temperature is 180-250℃, the reaction pressure is 1.0-4.0 MPa, and the holding time is 6-24 h; the stepwise drying process is as follows: first, dry at a low temperature of 60-80℃ for 24 h, and then heat up to 100-120℃ to dry to constant weight.

[0016] Further, in step S1, the pretreatment of the polycrystalline hybrid reinforcement phase and the construction of the gradient interface are completed, specifically as follows: First, hydroxylation etching is performed by mixing long polycrystalline fibers, short polycrystalline fibers, and mullite whiskers in a certain proportion, immersing them in a saturated calcium hydroxide solution, ultrasonically dispersing for 15-30 minutes, soaking for 2-4 hours, and then draining to obtain the hydroxylated hybrid reinforcement phase; then, a nanocrystalline seed layer is constructed by immersing the hydroxylated hybrid reinforcement phase in a calcium-silicon precursor solution and stirring at 25-40°C for 30-60 minutes. After filtration, the mixture is dried at 60-80℃ for 1-2 hours to obtain a modified hybrid reinforcing phase with a hydrated calcium silicate nanocrystal seed transition layer on the surface. The calcium-silicon precursor solution has a calcium to silicon molar ratio of 1:1, a soluble calcium salt concentration of 0.05-0.2 mol / L, a soluble silicon salt concentration of 0.05-0.2 mol / L, and a pH value adjusted to 11-12. In step S2, after the matrix mixture slurry is prepared, the modified hybrid reinforcing phase is added to the matrix mixture slurry, dispersed at high speed, and then... Interface modifier, foam stabilizer, and controllable foaming agent are mixed at low speed to obtain a composite slurry; the high-speed dispersion speed is 1500-3000 rpm for 15-30 min; the low-speed stirring speed is 200-300 rpm for 5-10 min; during hydrothermal synthesis, the wet preform is placed in a reactor, and the temperature is first increased to 160-180℃ at a rate of 1-1.5℃ / min, and held at this temperature and pressure for 2-4 h to activate the seed crystals and induce directional nucleation; then, at 0.5-1... The temperature is increased to 220-250℃ at a rate of ℃ / min, and held at that temperature and pressure for 10-20 hours to allow hydrated calcium silicate crystals to grow in situ on the fiber surface through a nanocrystalline seed transition layer, constructing a three-dimensional interpenetrating network structure and a hierarchical closed-cell structure. After naturally cooling to room temperature, the green body is removed. The step-by-step drying process is as follows: first, pre-drying at a low temperature of 50-60℃ for 3-4 hours to remove 70%-80% of the free water; then drying at 70-80℃ for 2-3 hours; and finally, drying at 100-120℃ to constant weight.

[0017] Compared with the prior art, the composite board based on hydrated calcium silicate and polycrystalline fiber and its preparation method of the present invention have the following advantages: 1. Strong interfacial bonding ensures mechanical properties: By introducing active nucleation sites through polycrystalline fiber surface modification and combining it with hydrothermal in-situ synthesis process, hydrated calcium silicate crystals are directionally grown on the fiber surface to form a chemically bonded interfacial structure. The interfacial bonding strength is enhanced through the gradient interfacial structure. At the same time, a three-dimensional interpenetrating network of fiber and crystal is constructed. Under stress, the fiber can effectively transfer the load and prevent crack propagation. Compared with unmodified fiber composite boards, the flexural strength is greatly improved; the fiber pull-out rate is reduced, and there is no obvious interfacial separation under stress.

[0018] 2. Balancing the requirements of lightweight, low thermal conductivity, and high strength of the board: By controlling the nanoporous structure through foam stabilizers and coordinating the uniform dispersion of fibers, the mechanical strength of the material is improved while maintaining a high porosity of 60%-85%. This achieves a dry density of 200-400 kg / m³ and a thermal conductivity as low as 0.035 W / (m•K). Furthermore, through a hierarchical closed-cell structure, the dry density of the board can be reduced to 180-250 kg / m³, and the thermal conductivity at 25℃ can be as low as 0.030 W / (m•K), while maintaining a flexural strength ≥2.5 MPa.

[0019] 3. Improved high-temperature service stability: Through high-temperature stable polycrystalline mullite / alumina fiber, combined with hydrothermally synthesized hard silica calcium stone matrix, both have excellent high-temperature resistance. The maximum service temperature of the composite board can reach over 1000℃, and the linear shrinkage rate after 3 hours of heat preservation at 1000℃ is ≤2%, with no powdering or cracking.

[0020] 4. Significant improvement in mechanical toughness and impact resistance: By combining a hybrid polycrystalline fiber system with a high-purity hard silica calcium stone matrix, the fracture toughness and impact resistance of the slab are greatly improved. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process for preparing a composite board based on hydrated calcium silicate and polycrystalline fiber in Embodiment 1 of the present invention.

[0022] Figure 2 This is a schematic diagram of the process for preparing a composite board based on hydrated calcium silicate and polycrystalline fiber in Embodiment 4 of the present invention. Detailed Implementation

[0023] The present invention relates to a composite board based on hydrated calcium silicate and polycrystalline fibers, comprising a board body composed of the following components by weight: 25-45 parts calcium source, 30-55 parts silicon source, 5-25 parts polycrystalline fibers, 0.5-3 parts interface modifier, 0.1-1 parts dispersant, 0.1-0.5 parts foam stabilizer, and 150-300 parts water. The calcium source and silicon source undergo a hydrothermal reaction to generate hydrated calcium silicate crystals, which interweave to form a porous matrix framework. The polycrystalline fibers are dispersed in the porous matrix framework, and the hydrated calcium silicate crystals and polycrystalline fibers form a three-dimensional interpenetrating network structure inside the board. The hydrated calcium silicate crystals grow in situ on the surface of the polycrystalline fibers, forming a chemical bonding layer with the polycrystalline fibers.

[0024] The calcium source is one or more of calcium oxide, calcium hydroxide, and carbide slag, and the effective calcium oxide content in the calcium source is ≥85% by mass; the silicon source is one or more of silica fume, silica, fly ash, diatomaceous earth, and quartz powder, and the active silica content in the silicon source is ≥80% by mass, with a particle size D50 of 1~10μm; the polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber; the polycrystalline fiber has a diameter of 25μm, a length of 15mm, and a crystal phase mass content of ≥85%. The content is ≥95%; the polycrystalline fiber is a modified polycrystalline fiber that has undergone surface modification treatment, wherein the surface modification treatment is silane coupling agent modification treatment or calcium hydroxide saturated solution hydration modification treatment; the interface modifier is one or more of silane coupling agent, aluminate coupling agent and titanate coupling agent; the dispersant is one or more of polycarboxylate dispersant, naphthalene sulfonate dispersant, sodium tripolyphosphate and sodium hexametaphosphate; the foam stabilizer is one or more of calcium stearate, sodium stearate, sodium dodecyl sulfate and methylcellulose.

[0025] The porous matrix framework has a porosity of 60%-85% and an average pore size of 50-200 nm.

[0026] The board body further includes 0.05-0.3 parts of a controllable foaming agent; the polycrystalline fiber is a polycrystalline hybrid reinforcing phase formed by mixing long polycrystalline fibers, short polycrystalline fibers and mullite whiskers, the short polycrystalline fibers and long polycrystalline fibers are composed of fibers of the same material, the crystalline phase mass content of the mullite whiskers is ≥95%, and the mass ratio of the long polycrystalline fibers, short polycrystalline fibers and mullite whiskers is 5~8:2~3:1~2; the hydrated calcium silicate crystals interweave to form a hierarchical closed-cell porous matrix framework, and the polycrystalline hybrid reinforcing phase is dispersed in the hierarchical closed-cell porous matrix framework; the surface of the polycrystalline hybrid reinforcing phase is provided with a hydrated calcium silicate nanocrystal seed transition layer, and the hydrated calcium silicate crystals grow directionally in situ on the fiber surface through the hydrated calcium silicate nanocrystal seed transition layer, forming a continuous gradient chemical bonding layer with the polycrystalline hybrid reinforcing phase.

[0027] The gradient chemical bonding layer undergoes a two-step pretreatment process. First, the hybrid reinforcing phase is hydroxylated and etched to introduce a large number of active hydroxyl groups onto the surface. Then, a uniform layer of hydrated calcium silicate nanocrystal seed is deposited in situ on the fiber surface using a calcium-silicon precursor solution, forming a continuous gradient transition interface. During the hydrothermal reaction, the hydrated calcium silicate crystals of the matrix grow directionally using the nanocrystal seed sites and integrate with the transition layer, achieving continuous chemical bonding from the polycrystalline fiber to the matrix hydrated calcium silicate, eliminating interfacial stress concentration, and significantly improving the interfacial bonding strength.

[0028] The hierarchical closed-cell structure of the hierarchical closed-cell porous matrix framework is controlled as follows: First-level nanopores are formed by regulating the foam stabilizer, which restricts the convection and thermal conduction of air molecules and achieves basic low thermal conductivity; Second-level micron closed pores are formed by the decomposition and release of gas by the controllable foaming agent during hydrothermal heating, which reduces the proportion of solid-phase framework, reduces material density and solid-phase thermal conductivity, and at the same time, the closed-cell structure can avoid air convection, further reducing the thermal conductivity; The two levels of pores work together to significantly reduce density while maintaining mechanical strength through the optimization of the framework structure, achieving a balance between density and thermal insulation performance.

[0029] Polycrystalline hybrid reinforcing phase achieves ternary hybrid reinforcement and toughening: long polycrystalline fibers construct a macroscopic three-dimensional skeleton, bear the main load, and improve the overall flexural strength of the material; short polycrystalline fibers fill the gaps between long fibers, refine the matrix grains, and reduce defects inside the matrix; mullite whiskers form bridges between fibers and the matrix, and pin and deflect microcracks inside the matrix, consuming the energy of crack propagation; through full-scale crack control at the macro, meso, and micro scales, the fracture toughness and impact resistance of the material are significantly improved.

[0030] The controllable foaming agent is one or more of ammonium bicarbonate and sodium bicarbonate; the nanocrystal seed transition layer is a porous active layer formed by uniform deposition of hydrated calcium silicate nanocrystals; the thickness of the nanocrystal seed transition layer is 50-200 nm.

[0031] The hierarchical closed-pore porous matrix framework includes primary nanopores and secondary micron-sized closed pores; the primary nanopores have a pore size of 50-200 nm and a porosity of 70%-80%; the secondary micron-sized closed pores have a pore size of 1-5 μm and a porosity of 20%-30%.

[0032] The long polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber, with a diameter of 2-5 μm, a length of 3-5 mm, and a crystalline phase mass content ≥95%; the short polycrystalline fiber is the same material as the long polycrystalline fiber, with a diameter of 2-5 μm, a length of 0.5-1 mm, and a crystalline phase mass content ≥95%; the mullite whisker has a diameter of 0.1-0.5 μm, a length of 5-20 μm, and an aspect ratio ≥20.

[0033] A method for preparing a composite board based on hydrated calcium silicate and polycrystalline fibers, the method comprising the following steps: S1. Polycrystalline fiber pretreatment: Surface modification treatment is performed on polycrystalline fibers to obtain modified polycrystalline fibers; S2. Preparation of composite slurry: Calcium source is added to water for digestion treatment, and after sieving, calcium hydroxide emulsion is obtained; silicon source and dispersant are added to the calcium hydroxide emulsion, and stirred evenly to obtain matrix mixture slurry; modified polycrystalline fiber is added to the matrix mixture slurry, dispersed evenly, interface modifier and foam stabilizer are added, and stirred evenly to obtain composite slurry; S3. Molding: The composite slurry is shaped to obtain a wet blank; S4. Hydrothermal synthesis: The wet green body is placed in a reaction vessel and a hydrothermal synthesis reaction is carried out to allow hydrated calcium silicate crystals to grow in situ on the surface of polycrystalline fibers, thereby obtaining the green body after the reaction. S5. Drying and shaping: The reacted green body is dried in steps to obtain the finished sheet body.

[0034] The surface modification treatment is a silane coupling agent modification treatment, specifically: immersing the polycrystalline fiber in a 1%-5% (w / w) silane coupling agent ethanol solution for 30-60 minutes, then drying at 80-120℃ for 24 hours to obtain modified polycrystalline fiber; or the surface modification treatment is a calcium hydroxide saturated solution hydration modification treatment, specifically: immersing the polycrystalline fiber in a calcium hydroxide saturated solution for 2-4 hours, then removing and draining to obtain modified polycrystalline fiber; the digestion treatment temperature is 40-60℃, the time is 15-30 minutes, and sieving is done using a 200-mesh sieve; the dispersion rotation speed is 1000-3000 rpm. The reaction time is 10-30 min at rpm; the water-to-solid ratio of the composite slurry is 3:1 to 6:1; the molding process is one of compression molding, sheet forming, or casting; the compression molding pressure is 0.5-2 MPa, and the holding time is 10-30 s; during hydrothermal synthesis, the reactor filling degree is 30%-50%, the heating rate is 12℃ / min, the reaction temperature is 180-250℃, the reaction pressure is 1.0-4.0 MPa, and the holding time is 6-24 h; the stepwise drying process is as follows: first, dry at a low temperature of 60-80℃ for 24 h, and then heat up to 100-120℃ to dry to constant weight.

[0035] In step S1, the pretreatment of the polycrystalline hybrid reinforcement phase and the construction of the gradient interface are completed, specifically as follows: First, hydroxylation etching is performed. Long polycrystalline fibers, short polycrystalline fibers, and mullite whiskers are mixed in a certain proportion, immersed in a saturated calcium hydroxide solution, ultrasonically dispersed for 15-30 minutes, soaked for 2-4 hours, and then drained to obtain the hydroxylated hybrid reinforcement phase. Next, a nanocrystalline seed layer is constructed. The hydroxylated hybrid reinforcement phase is immersed in a calcium-silicon precursor solution, stirred at 25-40°C for 30-60 minutes, and then filtered. The modified hybrid reinforcing phase with a hydrated calcium silicate nanocrystal seed transition layer on the surface is obtained by drying at 60-80℃ for 1-2 hours. The calcium-silicon precursor solution has a calcium to silicon molar ratio of 1:1, a soluble calcium salt concentration of 0.05-0.2 mol / L, a soluble silicon salt concentration of 0.05-0.2 mol / L, and a pH value adjusted to 11-12. In step S2, after the matrix mixture slurry is prepared, the modified hybrid reinforcing phase is added to the matrix mixture slurry, dispersed at high speed, and then an interface modifier is added. A composite slurry is obtained by mixing a foam stabilizer, a foaming agent, and a controlled foaming agent at low speed until homogeneous. The high-speed dispersion speed is 1500-3000 rpm for 15-30 min; the low-speed stirring speed is 200-300 rpm for 5-10 min. During hydrothermal synthesis, the wet preform is placed in a reactor and heated to 160-180℃ at a rate of 1-1.5℃ / min, and held at this temperature and pressure for 2-4 h to activate the seed crystals and induce directional nucleation. Then, the temperature is increased by 0.5-1℃... The temperature is increased to 220-250℃ at a rate of / min, and held at that temperature and pressure for 10-20h to allow hydrated calcium silicate crystals to grow in situ on the fiber surface through a nano-seed transition layer, constructing a three-dimensional interpenetrating network structure and a hierarchical closed-cell structure. After natural cooling to room temperature, the preform is removed. The step-by-step drying process is as follows: first, pre-drying at a low temperature of 50-60℃ for 3-4h to remove 70%-80% of the free water; then drying at 70-80℃ for 2-3h; and finally, drying at 100-120℃ to constant weight.

[0036] Example 1: like Figure 1 As shown, the composite board based on hydrated calcium silicate and polycrystalline fiber in this embodiment includes a board body. The raw materials for preparing the board body, by weight, are: 35 parts calcium hydroxide (effective CaO content 92%), 45 parts silica fume (active SiO2 content 95%, D50=2μm), 15 parts modified polycrystalline mullite fiber (diameter 3μm, length 2mm, crystal phase content 98%), 1.5 parts KH-550 silane coupling agent, 0.5 parts sodium tripolyphosphate, 0.3 parts calcium stearate, and 250 parts deionized water. The preparation method includes the following steps: S1. Polycrystalline fiber pretreatment: Polycrystalline mullite fibers are immersed in a 2% KH-550 ethanol solution for 45 minutes and then dried at 100℃ for 3 hours to obtain modified polycrystalline fibers. S2. Preparation of composite slurry: Add calcium hydroxide to deionized water at 50℃, stir and digest for 20 min, and pass through a 200-mesh sieve to obtain calcium hydroxide emulsion; add silica fume and sodium tripolyphosphate, stir at low speed for 15 min to obtain matrix mixture slurry; add modified polycrystalline fiber, disperse at high speed of 2000 rpm for 20 min to make the fiber uniformly dispersed; add KH-550 coupling agent and calcium stearate, continue stirring for 8 min to obtain a uniform composite slurry with a water-to-solid ratio of 5:1; S3. Molding: The composite slurry is injected into a flat mold and pre-pressed under a pressure of 1MPa for 20s to obtain a wet blank with a thickness of 10mm. S4. Hydrothermal synthesis: Place the wet green body into a high-pressure reactor, add deionized water to control the filling degree to 40%, heat to 230℃ at a rate of 1.5℃ / min, corresponding to a saturated steam pressure of 2.8MPa, and maintain the temperature and pressure for 12 hours. After the reaction is completed, allow it to cool naturally to room temperature and remove the green body. S5. Drying and shaping: The blank is first dried at a low temperature of 70℃ for 3 hours, and then the temperature is raised to 110℃ and dried to constant weight to obtain composite fireproof and heat-insulating board.

[0037] Example 2: This embodiment of the composite board based on hydrated calcium silicate and polycrystalline fiber includes a board body. The raw materials for preparing the board body, by weight, are: 30 parts calcium oxide (88% effective CaO content), 50 parts diatomaceous earth (85% active SiO2 content, D50=5μm), 10 parts modified polycrystalline aluminum silicate fiber (4μm diameter, 3mm length, 96% crystalline phase content), 1 part KH-560 silane coupling agent, 0.3 parts sodium hexametaphosphate, 0.2 parts methylcellulose, and 220 parts deionized water. The preparation method includes the following steps: S1. Polycrystalline fiber pretreatment: Immerse polycrystalline aluminum silicate fibers in a saturated calcium hydroxide solution for 3 hours, then remove and drain to obtain modified polycrystalline fibers. Preparation of S2 composite slurry: Calcium oxide was added to deionized water at 55℃ and stirred for 25 min to digest. The mixture was then passed through a 200-mesh sieve to obtain a calcium hydroxide emulsion. Diatomaceous earth and sodium hexametaphosphate were added and stirred at low speed for 20 min to obtain a matrix mixture slurry. Modified polycrystalline fibers were added and dispersed at high speed at 1500 rpm for 25 min to ensure uniform fiber dispersion. KH-560 coupling agent and methylcellulose were added and stirred for another 10 min to obtain a uniform composite slurry with a water-to-solid ratio of 4.4:1. S3. Molding: The composite slurry is formed by using a rotary screen forming machine to obtain a wet blank with a thickness of 12mm; S4. Hydrothermal synthesis: Place the wet green body into a high-pressure reactor, add deionized water to control the filling degree to 35%, heat to 240℃ at a rate of 1℃ / min, corresponding to a saturated steam pressure of 3.4MPa, and maintain the temperature and pressure for 10h. After the reaction is completed, allow it to cool naturally to room temperature and remove the green body. S5. Drying and shaping: The blank is first dried at a low temperature of 65℃ for 4 hours, and then the temperature is raised to 105℃ and dried to constant weight to obtain composite fireproof and heat-insulating board.

[0038] Example 3: The composite board based on hydrated calcium silicate and polycrystalline fiber in this embodiment includes a board body. The raw materials for preparing the board body, by weight, are: 40 parts of calcium carbide slag (effective CaO content 85%), 38 parts of silica (active SiO2 content 98%, D50=1μm), 18 parts of modified polycrystalline alumina fiber (diameter 2μm, length 1.5mm, crystalline phase content 99%), 2 parts of aluminate coupling agent, 0.8 parts of polycarboxylate dispersant, 0.4 parts of sodium dodecyl sulfate, and 280 parts of deionized water. The preparation method includes the following steps: S1. Polycrystalline fiber pretreatment: Polycrystalline alumina fibers are immersed in a 3% (w / w) aluminate coupling agent ethanol solution for 60 min and then dried at 120℃ for 2 h to obtain modified polycrystalline fibers. S2. Preparation of composite slurry: Add calcium carbide slag to deionized water at 45℃, stir and digest for 30 min, and pass through a 200-mesh sieve to obtain calcium hydroxide emulsion; add fumed silica and polycarboxylate dispersant, stir at low speed for 10 min to obtain matrix mixture slurry; add modified polycrystalline fiber, disperse at high speed of 2500 rpm for 15 min to make the fiber uniformly dispersed; add aluminate coupling agent and sodium dodecyl sulfate, continue stirring for 5 min to obtain a uniform composite slurry with a water-to-solid ratio of 5.6:1. S3. Molding: The composite slurry is cast into a wet blank with a thickness of 8mm. S4. Hydrothermal synthesis: Place the wet green body into a high-pressure reactor, add deionized water to control the filling degree to 45%, heat to 220℃ at a rate of 2℃ / min, corresponding to a saturated steam pressure of 2.3MPa, and maintain the temperature and pressure for 18h. After the reaction is completed, allow it to cool naturally to room temperature and remove the green body. S5. Drying and shaping: The blank is first dried at a low temperature of 80℃ for 2 hours, and then the temperature is raised to 120℃ and dried to constant weight to obtain composite fireproof and heat-insulating board.

[0039] Comparative Example 1: This comparative example uses a traditional pure microporous calcium silicate board without the addition of polycrystalline fibers. The other raw materials and proportions are completely the same as in Example 1. The preparation method is completely the same as in Example 1 except that the polycrystalline fiber pretreatment is not performed.

[0040] Comparative Example 2: This comparative example uses unmodified polycrystalline mullite fibers. The other raw materials and proportions are completely the same as in Example 1. The preparation method is completely the same as in Example 1 except that the fiber surface modification treatment is not performed.

[0041] The performance of the plates prepared in the examples and comparative examples was tested according to the following standards: 1. Dry density: GB / T10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials - protective hot plate method"; 2. Thermal conductivity: GB / T10294-2008, test temperature 25℃; 3. Flexural strength and compressive strength: GB / T5486-2008 "Test methods for inorganic rigid thermal insulation products"; 4. Combustion performance: GB8624-2012 "Classification of combustion performance of building materials and products"; 5. High-temperature linear shrinkage: GB / T5486-2008, test conditions: 1000℃ for 3 hours.

[0042]

[0043] As can be seen from the test results in Table 1, the sheet materials prepared in Examples 1 to 3 of this invention, with a dry density comparable to Comparative Example 1, exhibit a flexural strength increase of over 150% and a lower thermal conductivity, achieving a synergistic improvement in thermal insulation and mechanical properties. Compared to Comparative Example 2 (unmodified fiber), Example 1 shows a 60% increase in flexural strength and a 50% reduction in high-temperature linear shrinkage. This indicates that fiber surface modification and in-situ synthesis processes can significantly improve interfacial bonding and high-temperature stability. Finally, all examples achieve A1-level non-combustible combustion performance, exhibiting no pulverization or cracking at 1000℃, fully meeting the requirements for fireproofing and thermal insulation.

[0044] Example 4: like Figure 2 As shown, the composite board based on hydrated calcium silicate and polycrystalline fiber in this embodiment includes a board body. The raw materials for preparing the board body, by weight, are: 35 parts of calcium hydroxide (effective CaO content 92%), 45 parts of silica fume (active SiO2 content 95%, D50=2μm), 15 parts of polycrystalline hybrid reinforcing phase (9 parts of long mullite fiber, 4 parts of short mullite fiber, and 2 parts of mullite whiskers), 1.5 parts of KH-550 silane coupling agent, 0.5 parts of sodium tripolyphosphate, 0.3 parts of calcium stearate, 0.1 parts of food-grade ammonium bicarbonate, and 250 parts of deionized water.

[0045] The method for preparing composite boards based on hydrated calcium silicate and polycrystalline fibers in this embodiment includes the following steps: S1. Pretreatment of polycrystalline hybrid reinforced phase: Step 1: Hydroxylation etching: Long mullite fibers, short mullite fibers, and mullite whiskers are mixed in proportion, immersed in a saturated calcium hydroxide solution, ultrasonically dispersed for 20 minutes, soaked for 3 hours, removed and drained to obtain a hydroxylated hybrid reinforcement phase; The second step involves constructing a nanocrystalline seed layer: The hydroxylated hybrid reinforcing phase is immersed in a calcium nitrate-sodium silicate precursor solution with a calcium-silicon molar ratio of 1:1 (calcium salt concentration 0.1 mol / L, pH=11.5), stirred at 30°C for 45 min, filtered, and dried at 70°C for 1.5 h to obtain a modified hybrid reinforcing phase with a 100 nm thick hydrated calcium silicate nanocrystalline seed transition layer on the surface. S2. Preparation of composite slurry: Add calcium hydroxide to deionized water at 50℃, stir and digest for 20 min, and pass through a 200-mesh sieve to obtain calcium hydroxide emulsion; add silica fume and sodium tripolyphosphate, stir at low speed for 15 min to obtain matrix mixture slurry; add modified hybrid reinforcing phase, disperse at high speed at 2000 rpm for 20 min to make the fibers uniformly dispersed; add KH-550 coupling agent, calcium stearate, and ammonium bicarbonate, stir at low speed at 200 rpm for 8 min to obtain a uniform composite slurry with a water-to-solid ratio of 5:1. S3. Molding: The composite slurry is injected into a flat mold and pre-pressed under a pressure of 1MPa for 20s to obtain a wet blank with a thickness of 10mm. S4. Segmented temperature-controlled hydrothermal synthesis: Place the wet billet into a high-pressure reactor, add deionized water to control the filling degree to 40%, first raise the temperature to 170℃ at a rate of 1.5℃ / min, and hold for 3 hours; then raise the temperature to 230℃ at a rate of 1℃ / min, corresponding to a saturated steam pressure of 2.8MPa, and hold for 12 hours. After the reaction is completed, allow it to cool naturally to room temperature and remove the billet. S5. Step-by-step drying and shaping: The green body is first pre-dried at a low temperature of 55℃ for 3.5 hours, then dried at 75℃ for 2.5 hours, and finally heated to 110℃ to dry to constant weight to obtain the sheet body.

[0046] Example 5: The difference between this embodiment and Embodiment 4 is as follows: The raw materials are: 30 parts calcium hydroxide, 40 parts silica fume, 12 parts polycrystalline hybrid reinforcing phase, 1 part KH-550 silane coupling agent, 0.3 parts sodium tripolyphosphate, 0.2 parts calcium stearate, 0.2 parts food-grade ammonium bicarbonate, and 280 parts deionized water; the remaining process steps are the same as in Embodiment 4; the dry density of the preparation is 180 kg / m³.

[0047] Example 6: The difference between this embodiment and embodiment 4 is as follows: polycrystalline alumina fiber is used as the hybrid reinforcing phase matrix, the hydrothermal reaction temperature is 240℃, and the holding time is 15h; the rest of the formulation and process steps are the same as those in embodiment 4.

[0048] Next, performance tests were conducted on Examples 4 to 6, with Example 1 used as a comparative example. Example 1 differed from Examples 4 to 6 in the following ways: Example 1 did not undergo gradient interface modification, did not add whiskers or a controllable foaming agent, and did not employ a segmented hydrothermal process. The test results are shown in Table 2.

[0049] As shown in Table 2, the test results of Examples 4 to 6 compared to Example 1 (comparative example) are as follows: dry density decreased by 17.9%-35.7%, thermal conductivity decreased by 13.2%-21.1%. Flexural strength increased by 18.8%~25%, fracture toughness increased by 33.3%~77.8%, impact strength increased by 75%~125%, crack control was achieved across all scales, and mechanical toughness was significantly improved; fiber pull-out rate decreased from >20% to <8% (optimal <4%), and the gradient interface layer ensured interfacial bonding; linear shrinkage at 1000℃ / 1200℃ was significantly reduced, and the maximum service temperature was increased to 1200℃, making it suitable for ultra-high temperature conditions. As can be seen from the above: In Example 1, the fiber and the matrix are only physically-chemically bonded by a single coupling agent, and there is still an abrupt change at the interface, making it easy to debond and pull out under stress; Examples 4 to 6 construct a continuous gradient interface structure of polycrystalline fiber-nanocrystalline seed transition layer-matrix hydrated calcium silicate, and achieve a continuous gradient transition of interface chemical bonding in two steps, which improves the interface bonding strength, reduces the fiber pull-out rate, and greatly improves the stress transfer efficiency; Example 1 uses a single nanoporous structure, which cannot achieve both low density and high strength. At low density, the pores are prone to collapse, and the thermal insulation and mechanical properties cannot be deeply balanced. Examples 4 to 6 design a hierarchical closed-pore porous structure with nanopores and micron-sized closed pores. By synergistically controlling the pore morphology and distribution through in-situ stabilization and controllable foaming, the dry density and thermal conductivity can be reduced simultaneously while maintaining flexural strength. This solves the industry contradiction that low density reduces strength and high density affects thermal insulation performance.

[0050] Example 1 uses a single long fiber reinforcement system, which has limited crack propagation control and limited improvement in toughness and impact resistance. Examples 4 to 6 establish a ternary hybrid multi-level reinforcement system of long polycrystalline fibers, short polycrystalline fibers and inorganic whiskers to achieve full-scale crack control at the macro, meso and micro scales, and greatly improve fracture toughness and impact resistance.

[0051] The above embodiments are merely preferred embodiments of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention are included within the scope of the present invention.

Claims

1. A composite board based on hydrated calcium silicate and polycrystalline fibers, characterized in that: The material includes a board body, which is composed of the following components by weight: 25-45 parts calcium source, 30-55 parts silicon source, 5-25 parts polycrystalline fiber, 0.5-3 parts interface modifier, 0.1-1 part dispersant, 0.1-0.5 parts foam stabilizer, and 150-300 parts water. The calcium source and silicon source undergo a hydrothermal reaction to generate hydrated calcium silicate crystals. The hydrated calcium silicate crystals interweave to form a porous matrix framework. The polycrystalline fiber is dispersed in the porous matrix framework. The hydrated calcium silicate crystals and polycrystalline fiber form a three-dimensional interpenetrating network structure inside the board body. The hydrated calcium silicate crystals grow in situ on the surface of the polycrystalline fiber and form a chemical bonding layer with the polycrystalline fiber.

2. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 1, characterized in that: The calcium source is one or more of calcium oxide, calcium hydroxide, and carbide slag, and the effective calcium oxide content in the calcium source is ≥85% by mass; the silicon source is one or more of silica fume, silica, fly ash, diatomaceous earth, and quartz powder, and the active silica content in the silicon source is ≥80% by mass, with a particle size D50 of 1~10μm; the polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber; the polycrystalline fiber has a diameter of 25μm, a length of 15mm, and a crystal phase mass content of ≥85%. The content is ≥95%; the polycrystalline fiber is a modified polycrystalline fiber that has undergone surface modification treatment, wherein the surface modification treatment is silane coupling agent modification treatment or calcium hydroxide saturated solution hydration modification treatment; the interface modifier is one or more of silane coupling agent, aluminate coupling agent and titanate coupling agent; the dispersant is one or more of polycarboxylate dispersant, naphthalene sulfonate dispersant, sodium tripolyphosphate and sodium hexametaphosphate; the foam stabilizer is one or more of calcium stearate, sodium stearate, sodium dodecyl sulfate and methylcellulose.

3. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 1, characterized in that: The porous matrix framework has a porosity of 60%-85% and an average pore size of 50-200 nm.

4. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 1, characterized in that: The board body further includes 0.05-0.3 parts of a controllable foaming agent; the polycrystalline fiber is a polycrystalline hybrid reinforcing phase formed by mixing long polycrystalline fibers, short polycrystalline fibers and mullite whiskers, the short polycrystalline fibers and long polycrystalline fibers are composed of fibers of the same material, the crystalline phase mass content of the mullite whiskers is ≥95%, and the mass ratio of the long polycrystalline fibers, short polycrystalline fibers and mullite whiskers is 5~8:2~3:1~2; the hydrated calcium silicate crystals interweave to form a hierarchical closed-cell porous matrix framework, and the polycrystalline hybrid reinforcing phase is dispersed in the hierarchical closed-cell porous matrix framework; the surface of the polycrystalline hybrid reinforcing phase is provided with a hydrated calcium silicate nanocrystal seed transition layer, and the hydrated calcium silicate crystals grow directionally in situ on the fiber surface through the hydrated calcium silicate nanocrystal seed transition layer, forming a continuous gradient chemical bonding layer with the polycrystalline hybrid reinforcing phase.

5. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 4, characterized in that: The controllable foaming agent is one or more of ammonium bicarbonate and sodium bicarbonate; the nanocrystal seed transition layer is a porous active layer formed by uniform deposition of hydrated calcium silicate nanocrystals; the thickness of the nanocrystal seed transition layer is 50-200 nm.

6. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 4, characterized in that: The hierarchical closed-pore porous matrix framework includes primary nanopores and secondary micron-sized closed pores; the primary nanopores have a pore size of 50-200 nm and a porosity of 70%-80%; the secondary micron-sized closed pores have a pore size of 1-5 μm and a porosity of 20%-30%.

7. The composite board based on hydrated calcium silicate and polycrystalline fiber according to claim 4, characterized in that: The long polycrystalline fiber is one or more of polycrystalline mullite fiber, polycrystalline aluminosilicate fiber, and polycrystalline alumina fiber, with a diameter of 2-5 μm, a length of 3-5 mm, and a crystalline phase mass content ≥95%; the short polycrystalline fiber is the same material as the long polycrystalline fiber, with a diameter of 2-5 μm, a length of 0.5-1 mm, and a crystalline phase mass content ≥95%; the mullite whisker has a diameter of 0.1-0.5 μm, a length of 5-20 μm, and an aspect ratio ≥20.

8. A method for preparing a composite board based on hydrated calcium silicate and polycrystalline fibers, used to prepare the composite board based on hydrated calcium silicate and polycrystalline fibers as described in any one of claims 1 to 7, characterized in that: The method includes the following steps: S1. Polycrystalline fiber pretreatment: The surface of the polycrystalline fiber is modified to obtain modified polycrystalline fiber; S2. Preparation of composite slurry: Calcium source is added to water for digestion treatment, and after sieving, calcium hydroxide emulsion is obtained; silicon source and dispersant are added to the calcium hydroxide emulsion, and stirred evenly to obtain matrix mixture slurry; modified polycrystalline fiber is added to the matrix mixture slurry, dispersed evenly, interface modifier and foam stabilizer are added, and stirred evenly to obtain composite slurry; S3. Molding: The composite slurry is shaped to obtain a wet blank; S4. Hydrothermal synthesis: The wet green body is placed in a reaction vessel and a hydrothermal synthesis reaction is carried out to allow hydrated calcium silicate crystals to grow in situ on the surface of polycrystalline fibers, thereby obtaining the green body after the reaction. S5. Drying and shaping: The reacted green body is dried in steps to obtain the finished sheet body.

9. The method for preparing a composite board based on hydrated calcium silicate and polycrystalline fibers according to claim 8, characterized in that: The surface modification treatment is a silane coupling agent modification treatment, specifically: immersing the polycrystalline fiber in a 1%-5% (w / w) silane coupling agent ethanol solution for 30-60 minutes, then drying at 80-120℃ for 24 hours to obtain modified polycrystalline fiber; or the surface modification treatment is a calcium hydroxide saturated solution hydration modification treatment, specifically: immersing the polycrystalline fiber in a calcium hydroxide saturated solution for 2-4 hours, then removing and draining to obtain modified polycrystalline fiber; the digestion treatment temperature is 40-60℃, the time is 15-30 minutes, and sieving is done using a 200-mesh sieve; the dispersion rotation speed is 1000-3000 rpm. The reaction time is 10-30 min at rpm; the water-to-solid ratio of the composite slurry is 3:1 to 6:1; the molding process is one of compression molding, sheet forming, or casting; the compression molding pressure is 0.5-2 MPa, and the holding time is 10-30 s; during hydrothermal synthesis, the reactor filling degree is 30%-50%, the heating rate is 12℃ / min, the reaction temperature is 180-250℃, the reaction pressure is 1.0-4.0 MPa, and the holding time is 6-24 h; the stepwise drying process is as follows: first, dry at a low temperature of 60-80℃ for 24 h, and then heat up to 100-120℃ to dry to constant weight.

10. The method for preparing a composite board based on hydrated calcium silicate and polycrystalline fibers according to claim 8, characterized in that: In step S1, the pretreatment of the polycrystalline hybrid reinforcement phase and the construction of the gradient interface are completed, specifically as follows: First, hydroxylation etching is performed. Long polycrystalline fibers, short polycrystalline fibers, and mullite whiskers are mixed in a certain proportion, immersed in a saturated calcium hydroxide solution, ultrasonically dispersed for 15-30 minutes, soaked for 2-4 hours, and then drained to obtain the hydroxylated hybrid reinforcement phase. Next, a nanocrystalline seed layer is constructed. The hydroxylated hybrid reinforcement phase is immersed in a calcium-silicon precursor solution, stirred at 25-40°C for 30-60 minutes, and then filtered. The modified hybrid reinforcing phase with a hydrated calcium silicate nanocrystal seed transition layer on the surface is obtained by drying at 60-80℃ for 1-2 hours. The calcium-silicon precursor solution has a calcium to silicon molar ratio of 1:1, a soluble calcium salt concentration of 0.05-0.2 mol / L, a soluble silicon salt concentration of 0.05-0.2 mol / L, and a pH value adjusted to 11-12. In step S2, after the matrix mixture slurry is prepared, the modified hybrid reinforcing phase is added to the matrix mixture slurry, dispersed at high speed, and then an interface modifier is added. A composite slurry is obtained by mixing a foam stabilizer, a foaming agent, and a controlled foaming agent at low speed until homogeneous. The high-speed dispersion speed is 1500-3000 rpm for 15-30 min; the low-speed stirring speed is 200-300 rpm for 5-10 min. During hydrothermal synthesis, the wet preform is placed in a reactor and heated to 160-180℃ at a rate of 1-1.5℃ / min, and held at this temperature and pressure for 2-4 h to activate the seed crystals and induce directional nucleation. Then, the temperature is increased by 0.5-1℃... The temperature is increased to 220-250℃ at a rate of / min, and held at that temperature and pressure for 10-20h to allow hydrated calcium silicate crystals to grow in situ on the fiber surface through a nano-seed transition layer, constructing a three-dimensional interpenetrating network structure and a hierarchical closed-cell structure. After natural cooling to room temperature, the preform is removed. The step-by-step drying process is as follows: first, pre-drying at a low temperature of 50-60℃ for 3-4h to remove 70%-80% of the free water; then drying at 70-80℃ for 2-3h; and finally, drying at 100-120℃ to constant weight.

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